Project Abstract Primary hyperparathyroidism, often caused by a single adenoma (80-85%) or four-gland hyperplasia (10-15%), can lead to elevated parathyroid hormone (PTH) levels and resultant hypercalcemia. Surgical excision of offending lesions is the standard of care, as the removal of pathologic adenomas reduces PTH and calcium values to baseline and avoids the risk of associated morbidities like insulin resistance, dyslipidemia, low mineral bone density, and nephrolithiasis. The small size, variable location, and indistinct external features of parathyroid glands can make their identification quite challenging intraoperatively. Distinguishing them from adjacent fat, lymph tissue, or thymus tissue may be complicated further in previously operated necks. Patient prognosis depends heavily on complete resection of the involved parathyroid glands. The inability to accurately localize the parathyroid glands during parathyroidectomy and thyroidectomy procedures can prevent patients from achieving postoperative normocalcemia. There is a critical need for an improved intraoperative method for real-time parathyroid localization. The goal of this proposal is to develop new optical methods based on Dynamic Optical Contrast Imaging (DOCI) characterized by speed, low cost, and improved sensitivity and specificity, for enhancing intraoperative parathyroid localization. The imaging system leverages a novel realization of temporally dependent measurements of tissue autofluorescence that allow the acquisition of specific tissue properties over a large field of view. This system is optimized such that it can be used by surgeons at the time of resection surgery to localize parathyroid tissue and has been extensively validated in ex vivo samples. Companion histology has verified the sensitivity and specificity of the technique. In the proposed work we will reconfigure the imaging system for a large field of view (FOV), then pursue an intraoperative study using DOCI to localize parathyroid tissue. Companion visible imagery and histology will be analyzed at all stages of the work ensuring statistical diagnostic power of the technique. The goal of these surgeries is to remove the diseased thyroid or parathyroid tissues while minimizing risks to surrounding nerves and vessels. Noninvasive, real-time imaging methods that can accurately and efficiently identify parathyroid gland tissue in vivo and differentiate it from surrounding neck tissues would be transformative in gland localization. We hypothesize that the accuracy and efficiency of parathyroid resection will improve significantly when aided by our optical imaging technology. This intraoperative instrument would be the first of its kind, giving us the potential to significantly improve the rapid localization of parathyroid tissue, thus enabling the surgeon to preserve healthy tissue and improve patient outcomes.